1. Field of the Invention
The invention relates to a crankshaft bearing for a motor vehicle with a first bearing surface on the engine side and a second bearing surface on the crankshaft side, the latter surface being disposed in a sliding manner on the first.
2. Background of the Invention
In internal combustion engines, the crankshaft is used to convert the upward and downward motion of the pistons of the engine into a continuous rotary motion. For this purpose, the crankshaft is supported in the engine block allowing rotary motion. In the prior art, this is accomplished by means of first bearing surfaces, which are connected directly or indirectly to the engine block, and second bearing surfaces, which are connected directly or indirectly to the crankshaft, the surfaces sliding on one another.
Since most engine blocks are typically produced from aluminum and most crankshafts are produced from steel or spheroidal graphite iron, the crankshaft bearings are subject to temperature-dependent clearance due to the different thermal expansion coefficients of these materials.
At high engine temperatures, this clearance increases, potentially leading to disadvantageous oil leakage. If the temperatures are very low when the engine is started, on the other hand, the crankshaft may stick in the crankshaft bearing. One way of mitigating these problems is to use special bearing sleeves between the crankshaft and the engine block, these being composed in part of aluminum and in part of steel. The disadvantage with this solution, however, is the increased outlay for additional components and the additional weight of the steel elements.
The present invention provides a crankshaft bearing of simple and low-cost construction, which is functionally reliable under all operating temperature. The crankshaft bearing, according to the invention, for a motor vehicle has a first bearing surface on the engine side and a second bearing surface on the crankshaft side, the latter surface sliding on the first. It is distinguished by the fact that the first bearing surface is composed completely or partially of aluminum and the second bearing surface is composed completely or partially of ADI.
ADI is a cast iron containing spheroidal graphite, the abbreviation ADI standing for austempered ductile iron and the corresponding term in DIN EN 1564 being bainitic cast iron. In the automotive sector, the literature contains references to the use of ADI for a drive shaft component, for example, (EP 0 968 868 A1), for a camshaft (U.S. Pat. No. 5,028,281), and for a differential (U.S. Pat. No. 5,082,507). It has also been found possible to use ADI as a material for the bearing surface of a crankshaft if the corresponding bearing surface on the engine block is composed completely or partially of aluminum. In particular, it is possible with this combination of materials to obtain a crankshaft bearing that is robust in relation to temperature fluctuations, exhibiting neither oil leakage at high temperatures nor jamming at low temperatures.
One particular advantage of this combination of materials is that the first bearing surface, on the engine side, can be of one-piece construction with the engine block since engine blocks are generally likewise produced completely or partially from aluminum. It is therefore not necessary to provide a separate component or change the material to provide the first bearing surface.
Another advantage with the combination of materials envisaged is that the second bearing surface, on the crankshaft side, can also be of one-piece construction with the crankshaft. This means that the entire crankshaft can be made from ADI, and this likewise allows the elimination of additional components and hence a reduction in costs.
It is particularly advantageous if the abovementioned configurations are combined, that is to say the first bearing surface is of one-piece construction with the engine block and the second bearing surface is of one-piece construction with the crankshaft. This makes it possible to dispense completely with additional components, such as bearing sleeves, thereby minimizing both production costs and the weight of the crankshaft bearing.
Regarding the types and compositions available, the aluminum of the first bearing surface and the ADI of the second bearing surface are advantageously chosen so that the thermal expansion coefficients of the materials differ by less than 10%, preferably by less than 6%, from one another. Such small deviations between the thermal expansion coefficients ensure that the crankshaft bearing operates reliably over the entire temperature range encountered in practice.
The above advantages, other advantages, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.